Machine tools, such as CNC machines, use a plurality of tools to produce a machined product. Cutting tools, such as end mills and drills, are automatically changed during a machining operation. The cutting tools are typically held in tool holders which are automatically installed and removed from machine spindles, as needed. In order to maintain precise tolerances, the tool holder must be rigidly held within the spindle. If relative movement occurs between the spindle and tool holder, machining errors will result and machining tolerances will be compromised.
A tool holder of the type to which this invention pertains, includes a tapered shank which is received in a complementary-shaped spindle socket. In order to maintain machine tolerances, it is critical that the tapered shank of the tool holder be in intimate and substantially full contact with the spindle socket. If the tool holder shank is not in full contact with the spindle socket, relative movement may occur, especially under heavy machining, which will produce wear in the tool holder shank or the spindle socket or both.
In the tool holder of the type to which this invention pertains, a retention knob is threadedly received by the shank. The retention knob is engaged by a spindle gripper and holds the tool holder within the spindle during the machining operation. It is has been found, that installation of the retention knob may create a distortion or enlargement in the tool holder shank. The distortion is usually increased if the retention knob is overtightened. This distortion may prevent the tool holder shank from fully engaging the spindle socket when the tool holder is installed. If the tool holder shank is not in full contact with the spindle socket, relative movement between the tool holder and socket may occur. This relative movement will decrease machine tolerances increase cutting tool wear and produce wear in the tool holder and/or spindle.